power: supply: olpc_battery: Allow building the driver on non-x86

With the recent changes to the driver and addition of OLPC XO-1.75 EC
driver it is possible to use this driver on ARM-based XO laptops as
well.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>